This invention relates generally to the field of rotors for use in electric generators and motors. In particular, the invention relates to electric dynamo rotor assemblies having multiple magnetic poles mounted thereon.
Rotors in the past have utilized a field core assembly consisting of two pole piece members with triangular magnetic poles alternatively meshed together. This core assembly covers a rotor coil through which current is passed to generate magnetic flux. The stator and stator coil generate an alternating current as the rotor spins within a field of magnetic flux. The stator is in a position where there is a spatial gap radially between the rotor and the stator.
As is well known by those skilled in the art, it is beneficial to the electrical output of the generator if the spatial gap between the rotor and the stator is kept as small as possible. However, due to the magnetic and centrifugal forces on the pole piece members, they tend to deform in an outward direction during rotation, possibly coming into contact with the stator as the deformation bridges the spatial gap. Contact with the stator is undesired because it hinders the rotation of the rotor and can possibly damage the stator, the poles or both. Even slight damage can compromise the rotational balance of the rotor, thereby causing vibration and various other harmonically induced forces that can further damage the rotor or surrounding componentry. In order to avoid this contact, the spatial gap can be increased, thus reducing the output of the electrical machine.
U.S. Pat. No. 5,903,084 attempted to solve this problem by placing magnets between adjacent triangular poles, which prevented some flux leakage, and placing non-magnetic tape or banding around the outer periphery of the rotor assembly. This solution had its own shortcomings, in that some deformation still occurred. Also, in this position, the tape or banding had to be made of an expensive, non-magnetic material to prevent flux leakage from the opposing pole pieces of the rotor assembly. Furthermore, the additional material around the circumference of the rotor was placed in a groove cut in all of the pole pieces. This groove added to the gap space between the rotor and the stator, resulting in a reduction in output power of the electrical machine.
The present invention provides, in one embodiment, an axially turnable rotor for an electric generator. A rotor coil is encased within two pole piece members each having a plurality of flanged magnetic poles extending from a flat base face. Each of these flanged magnetic poles has a retaining structure on the opposite end from the flat base face. In the preferred embodiment of the invention, this retaining structure takes the form of a subflange. When the two pole piece members are meshed together around the rotor coil, the subflanges of each pole piece member extend beyond the flat base face of the opposing pole piece member, allowing for the introduction of a ring or other securing means upon the subflanges. In a further embodiment of the present invention, a plurality of permanent magnets is positioned under at least one of the flanged magnetic poles.
In another embodiment of the present invention, only one pole piece member is used, and it completely encases the rotor coil by itself.
The invention may also be embodied in a method for preventing the outward deflection of the flanged magnetic poles of the pole piece members during the rotation of the rotor. The method includes the steps of providing retaining structures on the ends of the flanged magnetic poles and securing the flanged magnetic poles by attaching a ring-shaped securing means to these retaining structures. In the preferred embodiment of the invention, the retaining structures take the form of subflanges. The securing means may also include fasteners or brackets. In yet a further embodiment of the method, the securing means may be secured to the subflanges by an adhesive, by cutting a groove in the subflange to fit the securing means, or by bending the subflange up after placing the securing means on the subflange, thereby locking it in place.
The present invention provides a number of advantages over the prior art. The securing means prevents the outward deflection of the flanged magnetic poles during rotation. This keeps the flanged magnetic poles from contacting the stator. Since the outward deflection of the flanged magnetic poles is substantially reduced, the electric generator can be constructed in a manner leaving a very small spatial gap radially between the magnetic portions of the rotor and the stator. A smaller spatial gap results in increased output of the electrical machine.
Another advantage of the preferred embodiment of this invention is the fact that each securing means contacts only one of the two magnetic pole pieces. This means that they contact only one magnetic polarity, either North or South. Because of this feature, the magnetic flux leakage is kept to a minimum. This feature allows the use of both magnetic and non-magnetic materials for the securing means, which in turn provides the user with a broad range of material choices. This invention is also easier to manufacture than the prior art.
Yet another advantage of the present invention is the fact that each securing means is positioned outside of the spatial gap between the rotor and the stator. This avoids the prior art problem of cutting a groove in the circumference of the rotor, which would increase the spatial gap and decrease the output of the electrical machine.
It is to be understood that both the preceding summary and the following detailed description are intended to be exemplary and explanatory and are intended to provide a further explanation of the invention claimed. The invention will best be understood by reference to the following detailed description read in conjunction with the accompanying drawings.